ABSTRACT
OBJECTIVE: Building on our previous study, showing a correlation between ferritin in serum and urine, we conducted a feasibility evaluation, measuring urinary ferritin as a potential noninvasive screening test for iron deficiency among NICU patients. STUDY DESIGN: This was a prospective analysis of paired serum/urine ferritin levels. We defined iron-limited erythropoiesis by a RET-He <5th percentile lower reference interval (<28 pg). RESULTS: We obtained 49 paired serum/urine samples from neonates judged as at-risk for iron deficiency. Urine ferritin ("corrected" for urine creatinine and specific gravity) correlated with serum ferritin (correlation coefficient of log10-transformed values 0.44). A corrected urine ferritin <12 ng/mL had a sensitivity of 82% (95% CI, 67-93%) and a specificity of 100% (CI, 66-100%) for detecting iron-limited erythropoiesis, with a positive predictive value of 100% (CI, 89-100%). CONCLUSIONS: Measuring urinary ferritin in NICU patients is feasible. Since low values identify iron-limitation, this could become a useful noninvasive screen.
